Engine systems may be configured with boosting devices, such as turbochargers or superchargers, for providing a boosted air charge and improving peak power outputs. The use of a compressor allows a smaller displacement engine to provide as much power as a larger displacement engine, but with additional fuel economy benefits. However, when the compressor operates under low air flow and/or high pressure ratio conditions, the compressor is prone to surge. For example, when an operator tips-out of an accelerator pedal, an engine intake throttle closes, leading to reduced forward flow through the compressor, and a potential for surge. Surge can lead to noise, vibration, and harshness (NVH) issues such as undesirable noise from the engine intake system. In extreme cases, surge may result in compressor damage.
Operating points of the compressor that may lead to compressor surge are indicated on a compressor map by a surge line. For example, an engine controller may determine that the compressor is operating under surge conditions when then the compressor operating point is to the left of the surge line. Currently, engine systems utilize a calibrated surge line provided by a vehicle manufacturer in order to determine surge conditions and set control actions (in order to increase compressor flow and decrease outlet pressure by adjusting a compressor recirculation valve (CRV) coupled across the compressor, for example) for surge mitigation.
However, the inventors herein have identified potential issues with such an approach. For example, the calibrated surge line does not take into account part to part variability and aging, which may have a significant effect on the location of the surge line. Further, environmental conditions, such as temperature, may influence surge line location. Still further, the manufacturer calibrated surge line may be calibrated conservatively in order to avoid surge for a majority of application. As a result, useable compressor map region may be reduced, and consequently, drivability may be sacrificed.
In one example, some of the above issues may be at least partly addressed by a method for an engine including a compressor, comprising: detecting a surge event of the compressor based on a frequency content of a throttle inlet pressure sensor located downstream of the compressor; and adapting a surge line of a compressor map stored in a controller of the engine based on a compressor pressure ratio and a corrected compressor flow during the surge event. By adjusting the surge line based on an operating point of the compressor, surge behavior under current vehicle operating conditions including adaptations to environmental conditions may be learnt.
As an example, adaptation of the surge line on the compressor map may be learnt in real-time during one or more drive cycles based on a frequency and/or amplitude of the signal from a throttle inlet pressure sensor located downstream of the compressor. For example, the surge line may be retarded in response to detecting a surge (based on TIP sensor signal) when the compressor is operating in a non-surge region (region to the right of the surge line) of the compressor map. Further, the surge line may be advanced in response to not detecting a surge (based on TIP sensor signal) during expected surge operating conditions on the compressor map. For example, during a tip-out greater than a threshold resulting in the compressor operating in the surge region (region to the left of the surge line) of the compressor map and not detecting surge (based on TIP sensor signal), the surge line may be advanced.
In this way, based on compressor operating points and detection of surge events during vehicle operating conditions, the surge line may be adapted in real-time. By adapting surge line in real-time, more accurate calibration of the surge line may be possible. As a result, surge mitigation/avoidance actions may be performed more accurately, thereby improving drivability and fuel economy.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.